Remote apparatus of distributed antenna system

ABSTRACT

A remote apparatus includes: a plurality of sub amplification units amplifying radio frequency (RF) signals of different frequency bands, respectively; a test signal generation unit generating test signals of a frequency band for any one sub amplification unit among the plurality of sub amplification units; a conversion unit converting intermodulation (IM) signals generated in response to the test signals into a plurality of conversion IM signals by using a conversion signal of which a frequency is swept; and a control unit determining a degree of an intermodulation distortion by the any one sub amplification unit based on signal levels of the plurality of the conversion IM signals.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/KR2015/013251, filed Dec. 4, 2015, and claims priority from KoreanPatent Application No. 10-2014-0194365 filed Dec. 30, 2014, the contentsof which are incorporated herein by reference in their entireties.

BACKGROUND

1. Field

The inventive concept relates to a remote apparatus of a distributedantenna system. More particularly, the inventive concept relates to aremote apparatus of a distributed antenna system which usesintermodulation (IM) signals converted by using a swept conversionsignal to determine a degree intermodulation distortion withoutfrequency correction of the IM signals.

2. Description of Related Art

Intermodulation represents a phenomenon in which an output frequencycomponent harmonized by the sum and the difference between harmonicfrequencies of two different input frequency signals is output duringprocessing a radio frequency (RF) signal through a non-linear element.

The intermodulation may be called intermodulation distortion (IMD) as adistorted factor that interferes with a signal. Among the IMDs, an IMDgenerated from a passive element is called passive IMD (PIMD) and sincethe PIMD degrades a communication quality, the PIMD has been on the riseas a primary interference cause in a recent communication system.

However, most measurement apparatuses of the PIMD are expensiveapparatuses and have a limit in efficiently measuring the PIMD.

SUMMARY

The inventive concept is directed to a remote apparatus of a distributedantenna system which uses intermodulation (IM) signals converted byusing a swept conversion signal to determine a degree intermodualtiondistortion without frequency correction of the IM signals.

According to an aspect of an embodiment, there is provided a remoteapparatus, includes: a plurality of sub amplification units amplifyingradio frequency (RF) signals of different frequency bands, respectively;a test signal generation unit generating test signals of a frequencyband for any one sub amplification unit among the plurality of subamplification units; a conversion unit converting intermodulation (IM)signals generated in response to the test signals into a plurality ofconversion IM signals by using a conversion signal of which a frequencyis swept; and a control unit determining a degree of an intermodulationdistortion by the any one sub amplification unit based on signal levelsof the plurality of the conversion IM signals.

In an example embodiment, wherein the control unit may determine aconversion signal having the highest signal level among the plurality ofconversion IM signals as a 3^(rd) IM signal and determine the degree ofthe intermodulation distortion by the any one sub amplification unitbased on the signal level of the 3^(rd) IM signal.

In an example embodiment, wherein the control unit may determine aconversion signal having the second highest signal level among theplurality of conversion IM signals as a 5^(th) IM signal and determinethe degree of the intermodulation distortion by the any one subamplification unit based on the signal levels of the 3^(rd) IM signal adthe 5^(th) IM signal.

In an example embodiment, wherein the plurality of sub amplificationunits may be connected to each other in a cascade structure.

In an example embodiment, wherein the IM signal may be transmitted tothe conversion unit through the any one sub amplification unit and atleast one sub amplification unit connected to a rear end of the any onesub amplification unit.

In an example embodiment, the remote apparatus may further include afirst switch unit is switched to transmit any one of a downlink signaland the test signal to a sub amplification unit at a frontmost end amongthe plurality of sub amplification units.

In an example embodiment, the remote apparatus may further include asecond switch unit is switched to receive any one of an uplink signaland the IM signal to a sub amplification unit at a rearmost end amongthe plurality of sub amplification units.

In an example embodiment, the remote apparatus may further include ameasurement signal extraction filter for passing only a conversion IMsignal to be measured among the plurality of conversion IM signals.

In an example embodiment, the remote apparatus may further include apower measurer measuring a signal level of the conversion IM signalpassed by the measurement signal extraction filter and transmitting ameasured result to the control unit.

In an example embodiment, wherein the plurality of respective testsignals may be continuous wave signals.

According to embodiments of the inventive concept, a remote apparatus ofa distributed antenna system uses intermodulation (IM) signals convertedby using a swept conversion signal to determine a degree intermodulationdistortion without frequency correction of the IM signals.

Further, a passive intermodulation distortion (PIMD) measurement unit isprovided in the remote apparatus and an operating mode to measure thePIMD through switching is provided to save time and cost required tomeasure the PIMD.

In addition, a degree of the intermodulation distortion by a specificsub amplification unit among a plurality of sub amplification unitsconnected in a cascade structure may be selectively determined.

BRIEF DESCRIPTION OF THE FIGURES

A brief description of each drawing is provided to more sufficientlyunderstand drawings used in the detailed description of the inventiveconcept.

FIG. 1 is a block diagram of a remote apparatus according to anembodiment of the inventive concept.

FIG. 2 is an exemplary diagram illustrating a detailed configuration ofa passive intermodulation distortion (PIMD) measurement unit illustratedin FIG. 1.

FIG. 3 is an exemplary diagram illustrating a detailed configuration ofan amplification unit illustrated in FIG. 1.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The inventive concept may be variously modified and have variousembodiments, so that specific embodiments will be illustrated in thedrawings and described in the detailed description. However, this doesnot limit the inventive concept to specific embodiments, and it shouldbe understood that the inventive concept covers all the modifications,equivalents and replacements included within the idea and technicalscope of the inventive concept.

In describing the inventive concept, in the following description, adetailed explanation of known related technologies may be omitted toavoid unnecessarily obscuring the subject matter of the inventiveconcept. In addition, numeral figures (for example, 1, 2, and the like)used during describing the specification just are identification symbolsfor distinguishing one element from another element.

Further, in the specification, if it is described that one component is“connected” or “coupled” the other component, it is understood that theone component may be directly connected to or may directly coupled theother component but unless explicitly described to the contrary, anothercomponent may be “connected” or “coupled” between the components.

Further, terms including “unit”, “er”, “member”, “module”, and the likedisclosed in the specification mean a unit that processes at least onefunction or operation and this may be implemented by hardware orsoftware or a combination of hardware and software.

In addition, it will be apparent that in the specification, componentsare just classified for each main function which each component takescharge of. That is, two or more components to be described below may beprovided to be combined into one component or one component may beprovided to be separated into two or more for each of more subdividedfunctions. In addition, each of the components to be described below mayadditionally perform some or all functions among functions which othercomponents take charge of in addition to the main function which eachcomponent takes charge of and some functions among the main functionswhich the respective take charge of may be exclusively charged andperformed by other components.

Hereinafter, embodiments of the inventive concept will be sequentiallydescribed in detail.

FIG. 1 is a block diagram of a remote apparatus according to anembodiment of the inventive concept. In FIG. 1, it is illustrated thatone remote apparatus 100 is communicatively coupled to a headendapparatus 20 to constitute a distributed antenna system that relayscommunication between a base station 10 and a user terminal (notillustrated), but the inventive concept is not limited thereto. Thedistributed antenna system may include a plurality of remote apparatuscommunicatively coupled to the headend apparatus 20 and in this case,other remote apparatuses may also have substantially the same structureas a remote apparatus 100 to be described below. Further, in FIG. 1, itis illustrated that one base station 10 is connected to the headendapparatus 20, but the inventive concept is not limited thereto and aplurality of base stations may be connected to the headend apparatus, ofcourse.

Referring to FIG. 1, the remote apparatus 100 according to theembodiment of the inventive concept may include an optical transceiverunit 110, a first switch unit 120, a second switch unit 130, a controlunit 140, a passive intermodulation distortion (PIMD) measurement unit150, an amplification unit 170, a signal branching unit 180, and anantenna ANT.

The optical transceiver unit 110 may be connected to the headendapparatus 20 through a predetermined transport medium, for example, anoptical cable and receive an optical signal from the headend apparatus20. Herein, the optical signal is transmitted from the base station 10and a downlink signal including a plurality of RF signals havingdifferent frequency bands may be a signal electric-to-optical convertedby the headend apparatus 20.

The optical transceiver unit 110 may optical-to-electric convert theinput optical signal into the downlink signal. That is, the opticaltransceiver unit optical-to-electric converts the optical signal torestore a base station signal which the headend apparatus 20 receivesfrom the base station 10.

The first switch unit 120 may switch a connection state among a firstterminal a connected to the optical transceiver unit 110, a secondterminal b connected to the PIMD measurement unit 150, and a thirdterminal c connected to the amplification unit 170 according to controlby the control unit 140.

In some embodiments, when the first terminal and the third terminal c ofthe first switch unit 120 are connected to each other, the opticaltransceiver unit 110 may transfer the downlink signal to theamplification unit 170.

In some embodiments, when the second terminal b and the third terminal cof the first switch unit 120 are connected to each other, the PIMDmeasurement unit 150 may transfer test signals to the amplification unit170.

The second switch unit 130 may switch a connection state among a firstterminal a′ connected to the optical transceiver unit 110, a secondterminal b′ connected to the PIMD measurement unit 150, and a thirdterminal c′ connected to the amplification unit 170 according to thecontrol by the control unit 140.

In some embodiments, when the first terminal a′ and the third terminalc′ of the second switch unit 130 are connected to each other, theoptical transceiver unit 110 may receive an uplink signal from theamplification unit 170.

In some embodiments, when the second terminal b′ and the third terminalc′ of the second switch unit 130 are connected to each other, the PIMDmeasurement unit 150 may receive an intermodulation (IM) signalgenerated in response to the test signals from the amplification unit170.

The control unit 140 may control the overall operation of the remoteapparatus 100. The control unit 140 may select any one operation modeamong operation modes of the remote apparatus 100, for example, adownlink mode, an uplink mode, and a PIMD measurement mode. The controlunit 140 may control the first switch unit 120 and the second switchunit 130 according to the selected operation mode.

In some embodiments, the control unit 140 may select the operation modein response to an input of a manager. In other embodiment, the controlunit 140 may select the operation mode in response to a control signaltransmitted from a management server, for example, a network managementsystem (NMS) server.

The PIMD measurement unit 150 may generate the test signals and theintermodulation (IM) signal generated in response to the test signals inorder to determine the degree of the intermodulation distortion by anyone among a plurality of sub amplification units 210_1 to 210_n includedin the amplification unit 170. In some embodiments, the IM signal may beanalyzed by the control unit 140.

A structure and an operation of the PIMD measurement unit 150 will bedescribed in detail with reference to FIG. 2.

The amplification unit 170 may include the plurality of subamplification units 210_1 to 210_n that amplifies corresponding RFsignals among the radio frequency (RF) signals of the differentfrequency bands included in the downlink signal or the uplink signal,respectively. The plurality of sub amplification units 210_1 to 210_nmay be connected in a cascade structure. A detailed configuration of theplurality of sub amplification units 210_1 to 210_n will be describedbelow with reference to FIG. 3.

The signal branching unit 180 may combine the plurality of RF signalsoutput from the plurality of sub amplification units 210_1 to 210_n,respectively. The signal branching unit 180 may transmit the pluralityof combined RF signals to other external apparatuses, for example, userterminals including a cellular phone, a smart phone, a tablet PC, andthe like through the antenna ANT. In some embodiments, the signalbranching unit 180 may be implemented as a multiplexer (MUX).

In FIG. 1, the control unit 140 and the PIMD measurement unit 150 areillustrated with being distinguished as separate blocks, but the controlunit 140 and the PIMD measurement unit 150 may be configured as onemodule according to an implementation example. Further, in someembodiments, the first switch unit 120 and the second switch unit 130may be configured as one module.

FIG. 2 is an exemplary diagram illustrating a detailed configuration ofa passive intermodulation distortion (PIMD) measurement unit illustratedin FIG. 1.

Referring to FIGS. 1 and 2, the PIMD measurement unit 150 may include atest signal generation unit 152, a combiner 153, a conversion signalgeneration unit 156, a conversion unit 158, a measurement signalextraction filter 160, and a power detector 162.

The test signal generation unit 152 may generate test signals of afrequency band for any one sub amplification unit among the plurality ofsub amplification units 210_1 to 210_n included in the amplificationunit 170 according to the control by the control unit 140. In this case,a first test signal generation unit 152-1 may generate a first testsignal and a second test signal generation unit 152_2 may generate asecond test signal. In some embodiments, a plurality of respective testsignals may be continuous wave signals.

Hereinafter, a case will be assumed and described, in which the testsignal generation unit 152 generates test signals of a frequency bandfor a second sub amplification unit 210_2 among the plurality of subamplification units 210_1 to 210_n.

The combiner 154 combines a first signal and a second signal generatedby the test signal generation unit 152 to transmit the combined signalsto the first switch unit 120.

The first switch unit 120 may connect the second terminal b and thethird terminal c to each other in a PIMD measurement mode and transmitthe test signals combined by the combiner 154 to a first subamplification unit 210_1 at a foremost end among the plurality of subamplification units 210_1 to 210_n. The test signals transmitted to thefirst sub amplification unit 210_1 at the foremost end are divided intothe sub amplification units 210_2 to 210_n connected to a rear end ofthe first sub amplification unit 210_1 to be transferred.

A detailed transmission path of the test signals will be described belowwith reference to FIG. 3.

In this case, the test signals is amplified by the second subamplification unit 210_2 to be transmitted to the antenna ANT throughthe signal branching unit 180. Therefore, the intermodulation (IM)signal may be generated as a reflection wave form. The generated IMsignal may be transferred to the second sub amplification unit 210_2from the antenna ANT through the signal branching unit 180. The IMsignal may be transmitted to the second switch unit 130 through thesecond sub amplification unit 210_2 and at least one sub amplificationunit 210_3 to 210_n connected to the rear end of the second subamplification unit 210_2.

The second switch unit 130 may connect the second terminal b′ and thethird terminal c′ to each other in the PIMD measurement mode andtransmit the received IM signal to the conversion unit 158 of the PIMDmeasurement unit 150.

The conversion signal generation unit 156 may transmit the conversionsignal of which the frequency is swept under the control by the controlunit 140 to the conversion unit 158.

The conversion unit 158 may convert the IM signal transmitted throughthe second switch unit 130 into a plurality of conversion IM signals byusing the frequency-swept conversion signal. The plurality of conversionIM signals converted by the conversion unit 158 may mean 3rd to n-th IMsignals, respectively. In some embodiments, the conversion unit 158 maybe implemented as a mixer.

The measurement signal extraction filter 160 may pass a conversion IMsignal to be measured of a signal level among the plurality ofconversion IM signals. In some embodiments, the measurement signalextraction filter 160 may be implemented as a band pass filter.

The power measurer 162 may measure the signal level of the conversion IMsignal passed by the measurement signal extraction filter 160 andtransmit a measured result to the control unit 140.

The control unit 140 may determine the degree of the intermodulationdistortion by the second sub amplification unit 210_2 based on thesignal levels of the plurality of conversion IM signals. In someembodiments, the control unit 140 may determine a conversion signalhaving the highest signal level among the plurality of conversion IMsignals as the 3rd IM signal and determine the degree of theintermodulation distortion by the second sub amplification unit 210_2based on the signal level of the 3rd IM signal. In other embodiment, thecontrol unit 140 may determine a conversion signal having the secondhighest signal level among the plurality of conversion IM signals as the5th IM signal and determine the degree of the intermodulation distortionby the second sub amplification unit 210_2 based on the signal level ofthe 3rd IM signal and the signal level of the 5th IM signal.

Hereinabove, the case is described as an example, in which the degree ofthe intermodulation distortion by the second sub amplification unit210_2 is determined, but the technical scope of the inventive concept isnot limited thereto.

FIG. 3 is an exemplary diagram illustrating a detailed configuration ofan amplification unit illustrated in FIG. 1. In FIG. 3, the first switchunit 120, the second switch unit 130, the signal branching unit 180, andthe antenna ANT are together illustrated for convenience of explanation.

Referring to FIGS. 1 to 3, each of the sub amplification units 210_1 to210_n may include a first distributor/combiner 211, a first filter 213,and a first amplification unit 215.

First distributor/combiners 211_1 to 211_n may divide the test signalstransmitted from the first switch unit 120 and transfers the dividedtest signals to the sub amplification units connected to rear endsthereof.

For example, the first distributor/combiner 211_1 of the first subamplification unit 210_1 may divide and transfer the input test signalsto the first distributor/combiner 211_2 of the second sub amplificationunit 210_2 and the first distributor/combiner 211_2 of the second subamplification unit 210_2 may divide and transfer the received testsignals to the first distributor/combiner (not illustrated) of the thirdsub amplification unit (not illustrated).

Meanwhile, although not illustrated in FIG. 3, each of the firstdistributors/combiners 211_1 to 211_n may include an amplifier andcompensate for loss depending on the division of the test signals byusing the amplifier. According to the implementation example, theamplifier may be implemented as a module apart from the correspondingfirst distributor/combiner among the first distributors/combiners 211_1to 211_n.

First filters 213_1 to 213_n may pass RF signals of correspondingfrequency bands among a plurality of frequency bands. The first filters213_1 to 213_n may have different pass bands.

Since the test signals correspond to the frequency band of any one subamplification unit among the plurality of sub amplification units 210_1to 210_n, all of the test signals may be interrupted in the filters ofthe sub amplification units other than the any one sub amplificationunit. For example, when the frequency of the test signals corresponds tothe frequency band of the second sub amplification unit 210_2, all ofthe test signals are interrupted in the first filters 213_1 and 213_3 to213_n of the residual sub amplification units 210_1 and 210_3 to 210_n.

The first filters 215_1 to 215_n may amplify the test signals passingthrough the first filter. First amplifiers 215_1 to 215_n may high poweramplifiers. The first amplifiers 215_1 to 215_n may transfer theamplified test signals to the signal branching unit 180.

For example, when the frequency of the test signals corresponds to thefrequency band of the second sub amplification unit 210_2, the testsignals passing through the first filter 213_2 of the second subamplification unit 210_2 are amplified by the first amplifier 215_2 andtransmitted to the antenna ANT through the signal branching unit 180.Therefore, the intermodulation (IM) signal may be generated as thereflection wave form. The generated IM signal may be transferred to thesecond sub amplification unit 210_2 from the antenna ANT through thesignal branching unit 180. The IM signal may be transmitted to thesecond switch unit 130 through the second sub amplification unit 210_2and at least one sub amplification unit 210_3 to 210_n connected to therear end of the second sub amplification unit 210_2.

Each of the sub amplification units 210_1 to 210_n illustrated in FIG. 3may include a second filter 212, a second distributor/combiner 214, anda second amplifier 216.

Second filters 212_1 to 212_n may filter input signals and transmit thefiltered signals to corresponding distributors/combiners among seconddistributors/combiners 214_1 to 214_n.

The second distributors/combiners 214_1 to 214_n may combine and outputthe signal output from the corresponding second filter among the secondfilters 212_1 to 212_n and a signal transferred from a sub amplificationunit connected to a front end thereof, in detail the second amplifier ofthe sub amplification unit connected to the front end thereof. Since thesecond distributor/combiner 214_1 of the first sub amplification unit210_1 does not include the sub amplification unit connected to the frontend thereof, the second distributor/combiner 214_1 will transfer onlythe signal output from the second filter 212_1 to a second amplifier216_1. The second distributor/combiner 214_2 of the second subamplification unit 210_2 will combine the signal output from the secondamplifier 216_1 of the first sub amplification unit 210_1 connected tothe front end thereof and the signal output from the second filter 212_2and transfer the combined signals to the second amplifier 216_1.Further, the second distributor/combiner 214_n of the n-th subamplification unit 210_n combines a signal transferred from the n-1-thsub amplification unit connected to the front end thereof and the signaloutput from the second filter 212_n and transfers the combined signalsto the second amplifier 216_n.

Meanwhile, although not illustrated in FIG. 3, each of the seconddistributors/combiners 214_1 to 214_n may include the amplifier andcompensate for loss depending on the combination of the signaltransferred from the sub amplification unit connected to the front endand the signal transferred from the corresponding second filter by usingthe amplifier. Further, each of the second distributors 214_1 to 214_nmay include an attenuator and control a gain of the signal transferredfrom the sub amplification unit connected to the front end thereof byusing the attenuator. According to the implementation example, theamplifier and/or the attenuator may be implemented as a module apartfrom the corresponding second distributor/combiner among the seconddistributors/combiners 214_1 to 214_n.

Second amplifiers 216_1 to 216_n may amplify a signal output from thecorresponding second distributor/combiner among the seconddistributors/combiners 214_1 to 214_n. The second amplifiers 216_1 to216_n may high power amplifiers. The second amplifiers 216_1 to 216_nmay transfer the amplified signal to the sub amplification unitconnected to the rear end thereof and the second amplifier 216_n maytransfer the amplified RF signal to the third terminal c′ of the secondswitch unit 130.

The second amplifier 216_1 of the first sub amplification unit 210_1will transfer the amplified RF signal to the second distributor/combiner214_2 of the second sub amplification unit 210_2. The second amplifier216_2 of the second sub amplification unit 210_2 will transfer theamplified RF signal to the second distributor/combiner 214_3 of thethird sub amplification unit 210_3 connected to the rear end thereof. Asthe signals amplified by the sub amplification units at the front endare sequentially combined in the sub amplification units at the rear endand thereafter, transferred up to the n-th sub amplification unit 210_nconnected to the rearmost end, the n_th sub amplification unit 210_namplifies the signal output from the second distributor/combiner 214_nto restore the amplified signal to the signal and transfer the restoredsignal to the input terminal c′ of the second switch unit 170.

Meanwhile, although not illustrated in FIG. 3, each of the subamplification units 210_1 to 210_n may further include an amplifier thatamplifies the signal input from the signal branching unit 180 andtransfers the amplified signal to the corresponding second filter. Inthis case, the amplifier may be a low-noise amplifier.

For example, when the frequency of the test signals corresponds to thefrequency band of the second sub amplification unit 210_2, as afeed-back path of the IM signal generated in the reflection signal form,the IM signal passes through paths such as the second filter 212_2, thesecond distributor/combiner 214_2, and the second amplifier 216_2 of thesecond sub amplification unit 210_2 and the second distributor/combiner214_3 and the second amplifier 216_3 of the third sub amplification unit210_3 from the antenna ANT through the signal branching unit 180 andfinally, the IM signal may be transmitted to the third terminal c′ ofthe second switch unit 130 through the second distributor/combiner 214_nand the second amplifier 216_n of the n-th sub amplification unit 210_n.

Hereinabove, the inventive concept has been described in detail withreference to a preferred embodiment, but the inventive concept is notlimited to the embodiment and various modifications and changes can bemade by those skilled in the art within the scope of the inventiveconcept.

What is claimed is: 1-10. (canceled)
 11. A remote apparatus comprising:a plurality of sub amplification units amplifying radio frequency (RF)signals of different frequency bands, respectively; a test signalgeneration unit generating test signals of a frequency band for any onesub amplification unit among the plurality of sub amplification units; aconversion unit converting intermodulation (IM) signals generated inresponse to the test signals into a plurality of conversion IM signalsby using a conversion signal of which a frequency is swept; and acontrol unit determining a degree of an intermodulation distortion bythe any one sub amplification unit based on signal levels of theplurality of the conversion IM signals.
 12. The remote apparatus ofclaim 11, wherein the control unit determines a conversion signal havingthe highest signal level among the plurality of conversion IM signals asa 3^(rd) IM signal and determines the degree of the intermodulationdistortion by the any one sub amplification unit based on the signallevel of the 3^(rd) IM signal.
 13. The remote apparatus of claim 12,wherein the control unit determines a conversion signal having thesecond highest signal level among the plurality of conversion IM signalsas a 5^(th) IM signal and determines the degree of the intermodulationdistortion by the any one sub amplification unit based on the signallevels of the 3^(rd) IM signal ad the 5^(th) IM signal.
 14. The remoteapparatus of claim 11, wherein the plurality of sub amplification unitsare connected to each other in a cascade structure.
 15. The remoteapparatus of claim 14, wherein the IM signal is transmitted to theconversion unit through the any one sub amplification unit and at leastone sub amplification unit connected to a rear end of the any one subamplification unit.
 16. The remote apparatus of claim 11, furthercomprising: a first switch unit is switched to transmit any one of adownlink signal and the test signal to a sub amplification unit at afrontmost end among the plurality of sub amplification units.
 17. Theremote apparatus of claim 11, further comprising: a second switch unitis switched to receive any one of an uplink signal and the IM signal toa sub amplification unit at a rearmost end among the plurality of subamplification units.
 18. The remote apparatus of claim 11, furthercomprising: a measurement signal extraction filter for passing only aconversion IM signal to be measured among the plurality of conversion IMsignals.
 19. The remote apparatus of claim 18, further comprising: apower measurer measuring a signal level of the conversion IM signalpassed by the measurement signal extraction filter and transmitting ameasured result to the control unit.
 20. The remote apparatus of claim11, wherein the plurality of respective test signals are continuous wavesignals.